Direct injection engines, which inject fuel into each cylinder directly, atomize the injected fuel using high injection pressure. To do so, such an engine employs an electric low-pressure pump to supply fuel from a fuel tank to a high-pressure pump, which is driven by the power of the engine, so that the high-pressure pump discharges high-pressure fuel to fuel injection valves.
Such a high-pressure pump includes a quantity control valve to open and close the suction port of the high-pressure pump and an electromagnetic valve to move the quantity control valve for the opening and closing. Energization of the electromagnetic valve is controlled to control a period over which the quantity control valve is closed and thereby control the quantity of fuel to be discharged by the high-pressure pump and thus the fuel pressure.
When the electromagnetic valve is being closed, its movable portion strikes its stopper portion, generating a vibration, which may lead to an unpleasant noise. A solution for this is described in Patent Literature 1 (JP 2010-533820 A). A current value to be used when an electromagnetic valve of a high-pressure pump is energized so as to be closed is a minimum current value that can close the valve, so that the valve closing speed is reduced and thereby the vibration generated during valve closing control is inhibited. To determine the minimum current value, an actual fuel pressure of a pressure reservoir that stores the high-pressure fuel supplied from the high-pressure pump is compared to a target fuel pressure. The minimum current value is determined on the basis of a current value at which the deviation of the actual fuel pressure from the target fuel pressure exceeds a threshold value.